Platinum(II), palladium(II) and gold(III) complexes containing 1,1,4-trisubstituted thiosemicarbazide dianion ligands

Article abstract of DOI:10.1016/S0020-1693(02)01257-4

Reactions of cis-[PtCl₂(PPh₃)₂] or [PdCl₂(PPh₃)₂] with Ph₂N-NHC(S)NHPh and excess triethylamine, in refluxing methanol gave the complexes [M{SC(=NPh)NNPh₂}(PPh₃)₂] containing thiosemicarbazide dianion ligands. An analogous gold(III) complex containing the cyclo-aurated anilinopyridine ligand was also synthesised. A single crystal X-ray diffraction study was carried out on the complex [Pt{SC(=NPh)NNPh₂}(PPh₃)₂] which confirmed the bonding of the thiosemicarbazide dianion ligand via sulfur and the nitrogen bearing the NPh₂ substituent. In contrast, reaction of Ph₂N-NHC(S)NHMe with cis-[PtCl₂(PPh₃)₂] and excess triethylamine gave the complex [Pt{SC(=NNPh₂)NMe}(PPh₃)₂], containing a Pt-NMe group, characterized spectroscopically.

Full text of DOI:10.1016/S0020-1693(02)01257-4

Inorganica Chimica Acta 343 (2003) 74ꢁ78
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www.elsevier.com/locate/ica
Platinum(II), palladium(II) and gold(III) complexes containing
1,1,4-trisubstituted thiosemicarbazide dianion ligands
William Henderson a,*, Clifton E.F. Rickard b
a Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton, New Zealand
b Department of Chemistry, University of Auckland, Private Bag 92019, Auckland, New Zealand
Received 13 March 2002; accepted 16 August 2002
Abstract
Reactions of cis-[PtCl2(PPh3)2] or [PdCl2(PPh3)2] with Ph2NÃ
the complexes [M{SC(ÄNPh)NNPh2}(PPh3)2] containing thiosemicarbazide dianion ligands. An analogous gold(III) complex
containing the cyclo-aurated anilinopyridine ligand was also synthesised. A single crystal X-ray diffraction study was carried out on
the complex [Pt{SC(ÄNPh)NNPh2}(PPh3)2] which confirmed the bonding of the thiosemicarbazide dianion ligand via sulfur and the
nitrogen bearing the NPh2 substituent. In contrast, reaction of Ph2NÃNHC(S)NHMe with cis-[PtCl2(PPh3)2] and excess
triethylamine gave the complex [Pt{SC(ÄNNPh2)NMe}(PPh3)2], containing a PtÃNMe group, characterized spectroscopically.
# 2002 Elsevier Science B.V. All rights reserved.
/
NHC(S)NHPh and excess triethylamine, in refluxing methanol gave
/
/
/
/
/
Keywords: Platinum(II), palladium(II) and gold(III) complexes; Thiosemicarbazide dianion ligands; X-ray diffraction
1. Introduction
platinum thiosemicarbazide complexes via hydrogen
bonding has attracted recent interest [9].
A number of complexes are known which contain
disubstituted
[RNHC(S)NHR?]2ꢀ, coordinated to platinum(II) form-
ing four-membered PtÃSÃCÃN ring systems. Examples
include the complexes 1 formed from symmetrical
thioureas RNHC(S)NHR [1ꢁ3] and 2, formally derived
thiourea
dianion
ligands,
/
/
/
/
from the cyanothiourea MeNHC(S)NHCN [4].
Thiourea dianion complexes of other metals are also
known, e.g. palladium(II) [5], molybdenum(IV) [6],
rhodium(III) [7] and ruthenium(II) [7]. In this paper
we report the synthesis of platinum(II), palladium(II)
and gold(III) complexes of the trisubstituted thiosemi-
2. Results and discussion
carbazide ligands Ph2NÃ
Ph2NÃNHC(S)NHMe (3b), which form similar com-
plexes to the thiourea analogues. While metal complexes
of thiosemicarbazones have attracted much interest [8]
there have been fewer studies on metal complexes of
thiosemicarbazides, though supramolecular assembly of
/
NHC(S)NHPh (3a) and
/
The reactions of cis-[PtCl2(PPh3)2] or [PdCl2(PPh3)2]
1,1,4-triphenylthiosemicarbazide
with
[Ph2NÃ
/
NHC(S)NHPh] (3a) and triethylamine base in hot
methanol gives high yields of the complexes 4a and 4b,
respectively, containing the thiosemicarbazide dianion
ligand. The platinum complex is bright yellow in colour,
while the palladium complex is deep maroon; the
* Corresponding author. Tel.: ꢂ
4219
E-mail address: w.henderson@waikato.ac.nz (W. Henderson).
/
64-7-856 2889; fax: ꢂ64-7-838
/
complexes give the expected intense [Mꢂ
their ES mass spectra, and satisfactory microanalytical
/
H]ꢂ ions in
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 1 2 5 7 - 4

W. Henderson, C.E.F. Rickard / Inorganica Chimica Acta 343 (2003) 74ꢁ
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78
75
data.
The 31P{1H} NMR spectrum of complex 4a showed
the expected AB pattern for two inequivalent PPh3
ligands coordinated to platinum, with phosphine reso-
nances at d 16.9 and 11.1 showing 1J(PtP) coupling
constants of 3156 and 3147 Hz, respectively. In compar-
ison, the diphenylthiourea-derived analogue 1a has
similar coupling constants of 3261 and 3103 Hz [1].
Along with the major signals above, there was a minor
species in the isolated product (approximately 5%
relative intensity), which also appeared as an AB
pattern, with coupling to 195Pt of 3038 and 3330 Hz,
consistent with S and N donor ligands. This species is
tentatively assigned as the isomeric product 5a, since in
the ES MS spectrum of the crude complex only a single
Fig. 1. Molecular structure of [Pt{SC(Ä
/
NPh)NNPh2}(PPh3)2] (4a)
with thermal ellipsoids at the 50% probability level.
Table 1
Selected
˚
(A)
bond
lengths
and
angles
(8)
for
[Pt{SC(ÄNPh)NNPh2}(PPh3)2] (4a) with estimated standard devia-
tions in parentheses
Bond lengths
PtÃN(1)
PtÃP(1)
P(1)ÃC(31)
P(1)ÃC(51)
P(2)ÃC(71)
SÃC
N(1)ÃN(2)
N(2)ÃC(11)
N(3)ÃC(21)
2.097(2)
2.3158(7)
1.826(3)
1.833(3)
1.828(3)
1.798(3)
1.412(3)
1.432(3)
1.411(4)
PtÃP(2)
PtÃS
2.2614(7)
2.3299(8)
1.848(3)
1.833(3)
1.832(3)
1.374(4)
1.401(4)
1.281(4)
[Mꢂ
/
H]ꢂ ion was observed (together with a very low
H]ꢂ ion). An alternative isomer, con-
P(1)ÃC(41)
P(2)ÃC(61)
P(2)ÃC(81)
N(1)ÃC
N(2)ÃC(1)
N(3)ÃC
intensity [2Mꢂ
/
taining a five-membered ring with a coordinated NPh2
group, is tentatively ruled out on the basis of poor
coordinating ability of tertiary arylamines. Recrystalli-
sation of the initially formed product by vapour
diffusion of diethyl ether into a dichloromethane solu-
tion of the complex yielded bright yellow crystals of
pure 4a. Isolated samples of the palladium complex 4b
were pure by 31P NMR, with no evidence for another
isomer. Complex 4b is assigned an analogous structure
to 4a, with a PdNNPh2 group.
In order to unambiguously characterize the mode of
bonding of the thiosemicarbazide ligand to the platinum
centre, a single-crystal X-ray diffraction study was
carried out on complex 4a. The molecular structure is
shown in Fig. 1, together with the atom numbering
scheme, while selected bond lengths and angles are given
in Table 1. The structure confirms the complex as a
thiosemicarbazide dianion complex, coordinated to
platinum through the sulfur and the nitrogen bearing a
substituted NPh2 group, forming a four-membered ring,
Bond angles
N(1)ÃPtÃP(2)
P(2)ÃPtÃP(1)
P(2)ÃPtÃS
CÃSÃPt
CÃN(1)ÃPt
162.39(7)
98.01(3)
93.31(3)
N(1)ÃPtÃP(1)
N(1)ÃPtÃS
P(1)ÃPtÃS
99.47(7)
69.08(7)
166.68(2)
115.2(2)
133.59(19)
123.9(2)
117.2(2)
128.8(2)
82.96(10) CÃN(1)ÃN(2)
103.51(16) N(2)ÃN(1)ÃPt
C(1)ÃN(2)ÃN(1)
N(1)ÃN(2)ÃC(11)
N(3)ÃCÃN(1)
N(1)ÃCÃS
119.2(2)
115.4(2)
127.0(3)
104.25(18)
C(1)ÃN(2)ÃC(11)
CÃN(3)ÃC(21)
N(3)ÃCÃS
bazone monoanions [10]. Burrows et al. [9] have
reported the structure of [(Ph2PCH2CH2PPh2)PtCl{SÄ
C(NHNMe2)(NHMe)]PF6, containing a neutral, S-
bonded trisubtituted thiosemicarbazide ligand. The
structure of 4a thus appears to be first of a thiosemi-
carbazide bonded as a dianion to a transition metal
centre.
/
analogous to the previous structure of [Pt{SC(Ä
NPh)NPh}(PPh3)2] [1]. This isomer is presumably
formed, as opposed to the alternative isomer [Pt{SC(Ä
/
/
Overall, the structural features of 4a are very similar
to the related diphenylthiourea dianion complex 1a [1].
NNPh2)NPh}(PPh3)2], because the NPh2 group is
sterically less bulky in the platinum coordination
environment than the Ph group alone. Examination of
the Cambridge Crystallographic Database (version 5.22,
October 2001) revealed only five structures containing
˚
Thus, the PtÃ
/
S [1a 2.331(1), 4a 2.3299(8) A], SÃ
/C [1a
˚
1.782(5), 4a 1.798(3) A] and CÄ
/
N [1a 1.277(6), 4a
˚
1.281(4) A] bonds are very comparable. However, the
metallacyclic CÃN and PtÃN bonds of 4a [1.374(4) and
2.097(2) A, respectively] are both considerably longer
/
/
the MÃ
/
SÃ
/
C(N)Ã
/
NN (Mꢃ
/
transition metal) four-mem-
bered ring system, all being complexes of thiosemicar-
˚

76
W. Henderson, C.E.F. Rickard / Inorganica Chimica Acta 343 (2003) 74ꢁ78
/
than the corresponding bonds in 1a [CÃ
N 2.054(3) A]. Furthermore, the metallacyclic N in 4a is
less planar than its counterpart in 1a, as shown by the
bond angle sums [1a 357.1, 4a 352.38]. The PtÃP bond
distances of 4a [cis to S 2.2614(7), trans to S 2.3158(7)
/
N 1.348(7), PtÃ
/
slight excess of Ph2NÃ
/
NHC(S)NHMe and triethylamine
˚
base in hot methanol gave complex 5b as a yellow solid
in high yield, which gave good microanalytical data, and
a single [Mꢂ
H]ꢂ ion in the positive ion ES mass
spectrum. However, NMR spectroscopic analysis indi-
cated that the opposite isomer to 4a had formed. The
/
/
˚
A] are both longer than their counterparts in 1a [cis to S
˚
2.247(1), trans to S 2.308(1) A].
presence of a PtÃ
/
NMe group was readily ascertained by
a resonance at d 2.43 in the 1H NMR spectrum,
showing coupling to both 31P (4.1 Hz) and 195Pt (29.9
Hz). These values compare very favourably with 1H
NMR data for other complexes with (Ph3P)2PtÃ
/
NMe
groups, such as [Pt{SC(ÄNMe)NMe}(PPh3)2] (1b) [d
/
2.27, 4J(PH) 4.29, 3J(PtH) 31.2] [3] and [Pt{SC(Ä
/
NCN)NMe}(PPh3)2] (2) [d 2.16, 4J(PH) 4.0, 3J(PtH)
31] [4]. In the case of complex 5b, the small size of the
methyl group compared to NPh2 appears to be effecting
isomerisation.
Using the same methodology as for the platinum and
palladium complexes above, reaction of the gold(III)
dichloride complex 6 with Ph2NNHC(S)NHPh and
triethylamine gave 7, which had a low solubility in
common organic solvents. The complex is also tenta-
tively assigned as having a coordinated NNPh2 group,
though the complex was too insoluble for NMR studies
(which would probably be of limited usefulness) and
single crystals could not be obtained. Gold(III) com-
plexes containing thiosemicarbazones as ligands have
been recently prepared by reaction of the gold(III)
complex 8 with a variety of thiosemicarbazones; the
In conclusion, trisubstituted thiosemicarbazide dia-
nion ligands show strong similarities to the related
thiourea dianion ligands, in bonding via S and N,
forming four-membered metallacycles. The observation
of isomerism dependent on ligand substituents suggests
that this may also occur in the thiourea analogues, and
this will be the topic of a subsequent investigation.
resulting products contain five-membered AuÃ
NÃN rings, and the original AuÃN bond is cleaved by
protonation [11]. Diphenylthiocarbazone (dithizone)
PhNHNHC(S)NÄNPh behaves in the same way [12].
/
SÃ
/
CÃ
/
3. Experimental
/
/
/
3.1. General experimental procedures
However, no gold(III) complexes of thiosemicarbazides
appear to have been characterized previously. In the
positive ion ES spectrum of 7, the [Mꢂ
H]ꢂ ion is
essentially the only ion at low cone voltages (20 V) or
very high cone voltages (140 V), while at intermediate
cone voltages (e.g. 80 V), other fragment ions in the
Electrospray mass spectra were recorded in MeOH
solution on a VG Platform II instrument with nitrogen
as the nebulising and drying gas. Identification of ions
was aided by comparison of experimental and theore-
tical [14] isotope distribution patterns. NMR spectra
were recorded on a Bruker AC300P instrument (1H,
300.1 MHz, 13C 75.5 MHz) or a Bruker DRX400
instrument (1H, 400.1 MHz, 13C 100 MHz) in CDCl3.
/
region m/z 400ꢁ
indicate the stability of the parent [Mꢂ
/
566 are observed. These observations
H]ꢂ ion,
/
compared to the small number of fragment ions which
are formed at elevated cone voltages. The stability of
gold(III) metallacyclic complexes bearing cyclo-aurated
ligands in ES analysis has been noted previously [13].
We subsequently wished to explore the effect of
substituting the phenyl group with a sterically less bulky
methyl, to provide an NMR spectroscopic handle upon
which to characterize the coordination geometry (the
Melting points were recorded using a ReichertꢁJung
/
hotstage apparatus, and are uncorrected. Reactions
were carried out in LR grade MeOH without further
purification, and without exclusion of air. Petroleum
spirits refers to the fraction of boiling point 60ꢁ80 8C,
/
and was used as supplied, while CH2Cl2 was distilled
from CaH2 prior to use.
presence of a PtÃ
/
NMe group can be readily determined
by NMR spectroscopy due to the presence of 195Pt and
1,1-Diphenylhydrazine hydrochloride (Aldrich) and
Et3N (BDH) were used as supplied. The complexes
[PtCl2(cod)] [15] and [PdCl2(cod)] [16] were synthesised
31P couplings). Reaction of cis-[PtCl2(PPh3)2] with a

W. Henderson, C.E.F. Rickard / Inorganica Chimica Acta 343 (2003) 74ꢁ
/
78
77
by the literature procedures and the complexes cis-
[PtCl2(PPh3)2] and [PdCl2(PPh3)2] synthesised from
them by ligand substitution with a stoichiometric
quantity of the phosphine in CH2Cl2 [17]. Complex 6
was prepared by the literature procedure [18].
The thiosemicarbazides Ph2NNHC(S)NHPh (3a) and
Ph2NNHC(S)NHMe (3b) were prepared by minor
modification of the literature procedure [19] involving
addition of Ph2NNH2 (prepared by treatment of the
hydrochloride salt with aq. KOH, and extraction of the
hydrazine with ether) to Et2O solutions of PhNCS or
3.4. Preparation of [Pt{SC(Ä
/
NNPh2)NMe}(PPh3)2]
(5b)
cis-[PtCl2(PPh3)2 (400 mg, 0.506 mmol) with
Ph2NNHC(S)NHMe (134 mg, 0.521 mmol) and Et3N
(1 ml) in MeOH (30 ml) was refluxed for 20 min to give
a clear yellow solution. Water (40 ml) was added, the
mixture cooled to r.t., and the yellow solid filtered,
washed with water (10 ml) and Et2O (2ꢄ
dried to give 5b (350 mg, 71%). M.p. 278ꢁ280 8C. Anal.
Found: C, 61.0; H, 4.5; N, 4.5. C50H43N3P2PtS requires
61.6; H, 4.4; N, 4.3%. ES MS (cone voltage 20 V) [Mꢂ
H]ꢂ (m/z 975, 100%). 31P{1H} NMR: d 18.8 [d, 1J(PtP)
/10 ml) and
/
MeNCS, respectively. Complex 3a, m.p. 180ꢁ
/
184 8C,
/
lit. 181 8C; 3b, m.p. 203ꢁ205 8C, lit. 203ꢁ204 8C.
/
/
2
1
2
3044, J(PP) 20] and 14.8 [d, J(PtP) 3213, J(PP) 20].
1H NMR: d 7.66ꢁ
6.85 (m, Ph) and 2.43 [d, PtNMe,
4J(PH) 4.1, J(PtH) 29.9].
/
3
3.2. Preparation of [Pt{SC(Ä
/NPh)NNPh2}(PPh3)2]
(4a)
3.5. Preparation of [Au{SC(Ä
/
NPh)NNPh2}(2-anp)]
To a pale yellow suspension of cis-[PtCl2(PPh3)2] (400
mg, 0.506 mmol) and Ph2NNHC(S)NHPh (3a) (168 mg,
0.527 mmol) in MeOH (30 ml) was added Et3N,
immediately giving a bright yellow suspension. The
mixture was refluxed for 10 min, water (10 ml) added
and the mixture cooled to room temperature (r.t.). The
bright yellow solid was filtered, washed with water (10
ml), cold MeOH (10 ml) and Et2O (10 ml), and dried to
(7)
Complex
6
(300 mg, 0.686 mmol) with
Ph2NNHC(S)NHPh (219 mg, 0.687 mmol) and excess
Et3N in MeOH (40 ml) was refluxed for 30 min, giving
an orange suspension. The mixture was cooled to r.t.,
the solid filtered, washed with water (10 ml), MeOH (10
ml) and Et2O (10 ml) and dried to give 7 as an orange
solid (426 mg, 91%). M.p. (dec.) 192ꢁ
C, 52.1; H, 3.5; N, 10.3. C30H24AuN5S requires: C, 52.7;
H, 3.5; N, 10.3%. ES MS (cone voltage 20 V) [Mꢂ
H]ꢂ
give 4a (484 mg, 92%). M.p. 270ꢁ
C, 63.5; H, 4.5; N, 4.3. C55H45N3P2PtS requires: C, 63.7;
H, 4.4; N, 4.1%. ES MS (cone voltage 20 V) [Mꢂ
H]ꢂ
/
274 8C. Anal. Found:
/
194 8C. Found:
/
/
(m/z 1037, 100%). The sample contained a small
quantity (approximately 5% by 31P NMR) of another
species, tentatively assigned as the isomer 5a on the basis
of 31P NMR data. Recrystallisation by vapour diffusion
of Et2O into a CH2Cl2 solution at r.t. gave pure 4a.
31P{1H} NMR, 4a: d 16.9 [d, 1J(PtP) 3156, 2J(PP) 23]
(m/z 684, 100%). The complex had insufficient solubility
in common solvents to allow characterization by NMR
spectroscopy.
3.6. Crystal structure determination of [Pt{SC(Ä
NPh)NNPh2}(PPh3)2] (4a)
/
1
2
and 11.1 [d, J(PtP) 3147, J(PP) 23]. For isomer 5a: d
2
17.5 [1J(PtP) 3038, J(PP) 21] and 12.8 [1J(PtP) 3330,
2J(PP) 21].
Bright yellow crystals were obtained by diffusion of
Et2O into a CH2Cl2 solution of the complex at r.t.
3.3. Preparation of [Pd{SC(Ä
/NPh)NNPh2}(PPh3)2]
(4b)
3.6.1. Crystal data
C55H45N3P2PtS, Mꢃ
group P21, aꢃ9.9066(1), bꢃ
105.844(1)8, Uꢃ2290.56(5) A , Tꢃ
2, rcalc
1.504 g cmꢀ3, m(Mo Ka)ꢃ
3.219 mmꢀ1, F(000)ꢃ
1040.
A total of 13 920 reflections were measured, 7441
unique (Rint 0.0211) which were all used in the
/
1037.03, monoclinic, space
[PdCl2(PPh3)2] (371 mg, 0.529 mmol) with
Ph2NNHC(S)NHPh (3a) (172 mg, 0.539 mmol) and
excess Et3N in MeOH (30 ml) was refluxed for 15 min to
give a deep red solution, plus some red solid. The
mixture was cooled to r.t., the red solid filtered, washed
/
/
18.4790(2), cꢃ
/
3
˚
˚
13.0065(2) A, bꢃ
/
/
/
150(2) K, Zꢃ
/
ꢃ
/
/
/
with water (2ꢄ
give 4b as a deep maroon solid (280 mg, 56%). M.p.
190ꢁ192 8C. Anal. Found: C, 69.3; H, 4.7; N, 4.3.
C55H45N3P2PdS requires: C, 69.7; H, 4.8; N, 4.4%. ES
/10 ml) and Et2O (10 ml) and dried to
ꢃ
/
refinement. A semi-empirical absorption correction
was carried out, Tmax and Tmin 0.5377 and 0.4999. Final
/
R indices: [I ꢀ
data: R1ꢃ0.0196, wR2ꢃ
the electron density map were 0.541 and ꢀ
The SHELX programs were used for all calculations [20].
/
2s(I)] R1ꢃ
0.0391. The largest residuals in
0.396 e Aꢀ3
.
/
0.0180, wR2ꢃ
/
0.0379. All
MS: (cone voltage 20 V) [Mꢂ
/
H]ꢂ (m/z 948, 100%).
/
/
31P{1H} NMR: d 30.5 [d, 2J(PP) 46] and 23.7 [d, 2J(PP)
46].
/

78
W. Henderson, C.E.F. Rickard / Inorganica Chimica Acta 343 (2003) 74ꢁ78
/
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4. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC No. 194952. Copies of this
information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2
(b) D. Kovala-Demertzi, J.R. Miller, N. Kourkoumelis, S.K.
Hadjikakou, M.A. Demertzis, Polyhedron 18 (1999) 1005;
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˜
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1EZ, UK (fax: ꢂ44-1223-336-033; e-mail: deposit@
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ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
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(f) L. Ze-Hua, D. Chun-Ying, L. Ji-Hui, L. Yong-Jiang, M. Yu-
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(1999) 2665.
Acknowledgements
We thank the University of Waikato for financial
support of this work, together with the New Zealand
Lottery Grants Board for a grant-in-aid for the pur-
chase of the mass spectrometer, and for the purchase of
precious metals. A generous loan of platinum from
Johnson Matthey plc is acknowledged. W.H. thanks Pat
Gread and Wendy Jackson for technical support and
Dr. Ralph Thomson for some of the NMR spectra.
[10] (a) F. Basuli, M. Ruf, C.G. Pierpont, S. Bhattacharya, Inorg.
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(b) A. Castineiras, E. Bermejo, D.X. West, A.K. El-Sawaf, J.K.
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(2000) 1120.
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